package com.faceye.core.util.id;

import java.io.Serializable;

/** Snowflake */
public class IDGenerator implements Serializable {
 
	/**
	    * 起始的时间戳
	    */
	    private final static long START_STMP = 1480166465631L;
	  
	    /**
	    * 每一部分占用的位数
	    */
	    private final static long SEQUENCE_BIT = 12; //序列号占用的位数
	    private final static long MACHINE_BIT = 5;  //机器标识占用的位数
	    private final static long DATACENTER_BIT = 5;//数据中心占用的位数
	  
	    /**
	    * 每一部分的最大值
	    */
	    private final static long MAX_DATACENTER_NUM = -1L ^ (-1L << DATACENTER_BIT);
	    private final static long MAX_MACHINE_NUM = -1L ^ (-1L << MACHINE_BIT);
	    private final static long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT);
	  
	    /**
	    * 每一部分向左的位移
	    */
	    private final static long MACHINE_LEFT = SEQUENCE_BIT;
	    private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
	    private final static long TIMESTMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;
	  
	    private long datacenterId;  //数据中心
	    private long machineId;    //机器标识
	    private long sequence = 0L; //序列号
	    private long lastStmp = -1L;//上一次时间戳
	  
	    public IDGenerator(long datacenterId, long machineId) {
	        if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
	            throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
	        }
	        if (machineId > MAX_MACHINE_NUM || machineId < 0) {
	            throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
	        }
	        this.datacenterId = datacenterId;
	        this.machineId = machineId;
	    }
	  
	    /**
	    * 产生下一个ID
	    *
	    * @return
	    */
	    public synchronized long nextId() {
	        long currStmp = getNewstmp();
	        if (currStmp < lastStmp) {
	            throw new RuntimeException("Clock moved backwards.  Refusing to generate id");
	        }
	  
	        if (currStmp == lastStmp) {
	            //相同毫秒内，序列号自增
	            sequence = (sequence + 1) & MAX_SEQUENCE;
	            //同一毫秒的序列数已经达到最大
	            if (sequence == 0L) {
	                currStmp = getNextMill();
	            }
	        } else {
	            //不同毫秒内，序列号置为0
	            sequence = 0L;
	        }
	  
	        lastStmp = currStmp;
	  
	        return (currStmp - START_STMP) << TIMESTMP_LEFT //时间戳部分
	                | datacenterId << DATACENTER_LEFT      //数据中心部分
	                | machineId << MACHINE_LEFT            //机器标识部分
	                | sequence;                            //序列号部分
	    }
	  
	    private long getNextMill() {
	        long mill = getNewstmp();
	        while (mill <= lastStmp) {
	            mill = getNewstmp();
	        }
	        return mill;
	    }
	  
	    private long getNewstmp() {
	        return System.currentTimeMillis();
	    }
 
  public static void main(String[] args) {
	  IDGenerator idWorker = new IDGenerator(9, 9);
    for (int i = 0; i < 1000; i++) {
      long id = idWorker.nextId();
      System.out.println(id);
    }
  }
}


